Osmosis has been used to treat industrial wastewaters, to concentrate landfill leachate, and to treat liquid foods in the food industry with low salinity content. Recent developments in material science also have allowed the use of osmosis in controlled drug release and in dialysis.
Compared to other industrial separation processes, osmosis has the advantage of operating at low to no hydraulic pressure; rejecting a wide range of contaminants; possibly having a lower membrane fouling propensity; and, using relatively simple, basic equipment.
Attempts have been made to use osmosis to generate power, but with limited success. One problem lies in the design of conventional semipermeable membrane elements, known commercially as modules or vessels. Currently available semipermeable membrane elements comprise tubular cylinders with relatively small bores, typically around 200 mm (8 inches) or less. A typical length of the currently available semipermeable membrane elements is only from about 1000-1500 mm.
Larger scale osmosis plants than those currently in existence, such as large scale power generation plants, would handle massive quantities of brine and produce large in-situ changes in flow rate within plant cells. Conventional osmosis hollow fiber or spiral wound membrane modules might be suitable for very small power generation applications and research and development work, but would not be efficient for use in large scale osmotic plants. First of all, a large scale osmotic process would comprise multiple cells and would require the use of hundreds of thousands, if not millions, of these relatively small conventional semipermeable membranes. Secondly, if such a massive number of conventional semipermeable membrane elements were used in a large scale osmotic process, the result would be an excessive pressure drop that would seriously impact plant efficiency and complicate plant operation and cost of maintenance.
More efficient semipermeable membrane elements are needed for use in designing large scale osmosis plants.